The present invention relates to a rigid coupling for pipes carrying pressurized fluid, allowing these pipes to be connected while pressurized fluid remains in one of them.
This coupling comprises, in a way known per se, a male element and a female element of which the ends that are to be connected are closed by valves. The male element, connected to a tool actuated by the fluid, contains pressurized fluid, while the female element connected to the fluid source is not under pressure.
Patent EP 0 847 511, in the name of the applicant, describes a coupling such as this in which the female element has a fixed external sleeve with an end for connection to a pipe supplying hydraulic fluid, and a slideable internal body containing the valve of the female element, a return spring being interposed between the external sleeve and the mobile internal body.
Each valve comprises a valve shutter that presses against the valve shutter of the other valve upon connection, a return spring pressing this shutter against a seat and a limit stop limiting the opening travel of the shutter.
The limit stop of the male element containing pressurized fluid is fixed, while the limit stop of the female element is slideably mounted in the female element so that it can occupy a forward fixed position in which the shutter is pressed against the limit stop when the male and female elements are connected, and so as to be able to retreat into the female element so as to allow the shutter associated therewith to retreat further than the aforementioned opening travel, the distance retreated corresponding substantially to the opening travel of the shutter of the male element.
The coupling also comprises means of locking and of returning the sliding limit stop into/in the forward position, these means allowing the retreating movement of the sliding limit stop upon connection of the male and female elements, and locking the sliding limit stop in the forward position once this connection has been made.
In a coupling such as this it is necessary to allow the mobile internal body to move in and out with respect to the fixed external sleeve. For this reason, it is common practice for the internal body that can move inside the fixed external sleeve to be “hydraulically balanced”, that is to say to use relationships between pressures and surface areas such that the sum of the forces generated by the pressure effects cancel each other out.
The return spring acting on the mobile internal body is capable of compensating for the small potential difference in forces that may be due to manufacturing tolerances manifested in the form of different diameters and different levels of friction.
Here, the technique used is the one known as “differential balancing”.
The central fluid stream is continuous. Three sealing members are used, two of identical diameter D1 and a third of a higher diameter D2 such that D2/D1=√2. This relationship allows the sealing cross section of small diameter D1 to be the same as the cross section of the annulus formed between the small diameter D1 and the large diameter D2.
The supply of pressurized fluid to the annulus between the large and small diameters is achieved via a through-hole passing through the mobile internal body.
The forces exerted on the two small-diameter sealing members and on the annulus between the large and small diameter are of the same magnitude but of opposite directions, thus balancing the position of the mobile internal body in the fixed external sleeve at a location predefined by the limit stops of the return spring that returns the internal body.
This technique is economically attractive as to the production of the mechanical parts and displays good hydrodynamic characteristics, but the mechanical relationship between the mobile internal body which notably bears the female shutter and the fixed external sleeve is complicated to achieve.
To achieve this mechanical relationship, the means for locking and for returning the sliding limit stop in/into the forward position usually comprise mobile sleeve tubes internal and external to the mobile internal body of the female element, and connected to one another via balls or pegs passing through the mobile internal body.
These elements both balance (in the hydraulic sense) the positions of the shutters of the male and female elements in a position such that the circuit is open to the hydraulic fluid, and allow the shutter to effect an overtravel inside the female element in order mechanically to lock the male and female elements in spite of the approximately 3 to 4 mm protrusion of the shutter of the male element, which protrusion is due to the pressurized fluid contained therein.
Because the male and female elements are mechanically connected and locked, the opening of the hydraulic circuit, and therefore the balancing of the shutters of the male and female elements, is done by subjecting the female element to the hydraulic line pressure until such point as the pressure therein is enough to counter the pressure in the male element and open the valve thereof.
This arrangement calls for a great many components and thus entails a great deal of accuracy in producing and assembling these components, to the detriment of the overall cost of the product.